The FBI has launched an investigation into an online protest that allegedly took down numerous Web sites belonging to antipiracy and entertainment groups, as well as the U.S. Copyright Office, a source with knowledge of the probe told CNET today.

Over the past two months, a group calling itself "Anonymous," with links to the 4chan Web forum and image board, has launched distributed denial-of-service attacks (DDoS) against Web sites operated by the Motion Picture Association of America, The Recording Industry Association (RIAA), Hustler magazine, rocker Gene Simmons, The British Phonographic Industry, and other similar groups in France, Australia, Spain and elsewhere.

A DDoS attack describes hitting a Web site with enough traffic to overwhelm the site's servers.

While one of the 4chan group's most recent attacks came last week against the Copyright Office, it is believed that the FBI began asking questions prior to that, said the source. Since the Copyright Office attack, however, FBI agents have begun working closely with many of the organizations attacked, the source said.

While there are reports that Anonymous plans to wind down the attacks, they are the latest sign that the animosity between copyright owners and file sharers is turning white hot as they battle for control of Web distribution. According to several messages from those claiming to speak for Anonymous, the group said it is motivated by protecting the free flow of information and that copyright is a form of censorship. Copyright owners argue that these groups are pseudo freedom fighters who are trying to justify theft. They say the only people losing anything in this struggle are those who make movies, software, music, and other intellectual property pilfered with the help of the Internet.

Just how much damage the attacks caused is unclear. Many of the targets hit provide little more than information about the organizations. However, the Copyright Office maintains records of copyright ownership, issues copyrights, and assists the U.S. Congress in developing copyright policy. As part of the Library of Congress, the Copyright Office is under the purview of the U.S. government's executive branch.

Matthew Raymond, a spokesman for the U.S. Library of Congress, which oversees the Copyright Office, said in an e-mail that the DDoS attack "significantly degraded the ability of users to access that server." FBI representatives did not respond to interview requests.

Participating in a DDoS attack can mean prison and fines.

"It's troubling that these groups seem more concerned about the rights of those who steal and copy films, music, books and other creative resources than the rights of American workers who are producing these products."

--MPAA spokesman on EFF

Last week, Mitchell L. Frost, 23, was sentenced to 30 months in prison after launching DDoS attacks in 2006 and 2007 against the Web sites of former presidential candidate Rudy Giuliani and political commentators Bill O'Reilly and Ann Coulter. In May, Frost pleaded guilty to causing damage to a protected computer system and possessing unauthorized access devices.

The DDoS attacks have occurred against a backdrop of increasing litigation by independent film and porn studios against individual file sharers, and as the music industry pursues two high profile file-sharing cases.

Earlier this year, a group of indie film companies, including Voltage Pictures, makers of the Oscar-winning motion picture, "The Hurt Locker," began filing copyright complaints in federal court against thousands of accused illegal file sharers. More recently, adult film studios, such as Hustler and Third World Media, followed suit and filed similar lawsuits.

Also this year, the RIAA, the trade group for the four largest record labels, won court decisions that resulted in the dismantling of LimeWire, one of the country's most popular file-sharing networks. Last week, the RIAA also saw a jury decide that Jammie Thomas-Rasset, an accused file-sharing mother from Minnesota, should pay $1.5 million in damages to the RIAA.

Meanwhile, as some on the file-sharing side have lashed out against the entertainment sector's attempts to enforce copyright, which they claim limits free speech, some copyright owners say the Anonymous group and supporters are hypocrites. They note that the DDoS attacks do little more than silence dissenting opinion.

When Gene Simmons, bass player for the iconic rock band Kiss, spoke out recently against illegal file sharing, his site, Genesimmons.com suffered outages as a result of a DDoS attack by Anonymous.

People supportive of the entertainment industry took the opportunity to ask where was the Electronic Frontier Foundation, the American Civil Liberties Union and other free-speech proponents when their sites were being gagged by Anonymous' traffic. EFF advocates for Internet users and tech companies and is typically at odds with entertainment companies over copyright issues.

"The silence here is deafening," said RIAA spokesman Jonathan Lamy. "Where's the outrage? Apparently, not all First Amendment free speech rights are created equal. At best, it's convenient indifference. At worst, it's quiet cheerleading."

A spokesman for the MPAA said: "It's troubling that these groups seem more concerned about the rights of those who steal and copy films, music, books, and other creative resources than the rights of American workers who are producing these products."

Rebecca Jeschke, an EFF spokeswoman fired right back: "We generally don't comment on DDoS attacks, even when they happen to us. DDoS attacks get in the way of people seeing content they want to see on the Internet, and of course that's not something we support. But we don't comment on them in part because it gives these folks what they want--attention for their stunts. As for the entertainment industry calling on us to criticize it? This is just silly PR gamesmanship, used in place of talking about the real issues of copyright at play here."

Jeschke's statement is reflective of the controversy the DDoS attacks have stirred even among some of file sharing's staunchest supporters.

Mike Masnick, founder of the blog Techdirt, wrote in September that the attacks were "dumb" and "don't make any real point." The tech news site, Ars Technica, has also been critical of the DDoS campaign.